The US military is "reasonably certain" that the extremist Jihadi John was killed in an air strike aimed at the notorious British killer.

US military spokesman Colonel Steve Warren said it would take "some time" to confirm the death of the extremist - real name Mohammed Emwazi - who was targeted in the Syrian stronghold of Islamic State (IS).

David Cameron has hailed the apparent death of Jihadi John as a "strike at the heart" of the extremist group.

But Labour leader Jeremy Corbyn said it would have been "far better" if Emwazi had been brought to justice in the courts for his "callous and brutal crimes".

Col Warren, the spokesman for the operation tackling IS, told reporters it was not an "exact science" but the intelligence gave the US "great confidence" that the individual targeted was indeed Emwazi, who he described as the "face" of IS.

"Now we are using the same intelligence capabilities to verify that the individual we killed was in fact Jihadi John," Col Warren said. The "high value individual (HVI)" is believed to have been killed along with an associate - or "worst best friend" - who may have been the driver of the car they were in when it was attacked with a Hellfire missile fired from a drone.

Speaking from Baghdad, Col Warren said: "For us it was a fairly routine HVI strike."

Although Emwazi was not thought to be a major tactical figure within the ranks of IS his appearance in a series of videos apparently showing the brutal murder of several hostages including Britons Alan Henning and David Haines meant he had propaganda value for the extremist group.

Col Warren said: "Jihadi John was somewhat of an Isil celebrity, if you will, kind of the face of the organisation in many senses.

"So there is certainly a significant blow to the prestige of Isil.

"But Jihadi John was not a major tactical figure or an operational figure."

Col Warren described Emwazi as a "human animal" and "killing him is probably making the world a little bit better place".

The Prime Minister said the US drone attack targeting Emwazi was an "act of self-defence" and "the right thing to do".

He was backed by the chairman of the Intelligence and Security Committee (ISC), who said there was a "sound legal basis" for the air strike in the Syrian stronghold of the terror group, which is also known as Isil or Daesh.

In a statement delivered outside 10 Downing Street, Mr Cameron stressed it was not yet absolutely certain that the "barbaric murderer" was dead.

"If this strike was successful it will be a strike at the heart of Isil," the Prime Minister said. "And it will demonstrate to those who would do Britain harm, we have a long reach."